member_of and part_of with pipe scoped contexts don't sort

[azaroth42]

Because

• member_of isn't properly specified, because part_of is hard coded
• part_of goes to the end (not bad, normally) because it gets rewritten to part_of|Pxxx_bla_bla so that the documentation popup knows which predicate it is, and the | form isn't in the key order hash